How did you calculate the aluminum head at 11.5 SCR? I figured it would go from 9.0 to around 9.8.
I don't recall, that was 6 months ago, my notes are gone.
Oh I get it;
It looks like I just entered 11.5 into the calculator to get the VP into the 140s where the fun starts.
My 360 came in at 11.3 Scr easy enough
At 367 cubes/752cc per cylinder, 11.5 would be 71.6cc max total chamber volume. I think the aluminum magnum heads are 58cc, plus 5 in the eyebrows, zero deck and 8.6 in the FelPros comes to 71.6 imagine that.
So that's probably how I got it.
Because VP is low rpm performance indicator,
VP only matters if
1) you have a manual trans and lo-performance gears, or
2) you have an automatic with a low-stall TC and lo-po gears
By 3000 to 3500 depending on the combo, VP is no longer a performance factor.
With a manual trans;
and the typical 3.55s, 3000 rpm in first gear is ~26 mph, so any time you are driving below that, VP begins to be important. And the slower you drive, the more important it will become. So obviously, most of the time, when you take off, the engine will NOT be at 3000 rpm,lol. And the more VP you have, the less throttle you will have to use to get moving.
Then there is cruising speed; the more VP you have, the less throttle you will need to cruise at, so the potential for best fuel economy is increased.
Next is second gear. 30mph is ~2540rpm . So say you are cruising along, and you want to accelerate, but you don't want to downshift to get 30@3520, cuz you just want to pick up the pace a lil. Well if your VP is down at 120, it's gonna take a lotta throttle to make some power; whereas if your VP is in the 140s, the car will practically leap ahead.
Ok now hang on; We can use that to our advantage. With the higher VP, the take off is easier and more rapid with the same throttle...... so then we could use less rear gear, and pick up some fuel economy at cruising speed.
Or if you think about it from the other side, you won't have the added expense of a bigger rear gear.
So if you combine this thinking;
let's say it costs you $1000 to pump up your VP into or close to the 140s. But you don't have to buy/ install gears (assuming you have at least 3.23s), so you save about 450 on that deal. If you have an automatic, you may also get by with the stall you now have, so now you are sneaking up on the break-even point. Next consider how much money you are gonna save by getting 2/3 or more mpgs on the hiway, over the life of the engine. And finally consider how much easier that extra torque ( cuz that is what the extra VP is pointing to) is gonna make your life because you don't always have to mash the pedal. With the higher cylinder pressure comes an across-the-board power increase through out the rpm range, every part of it will have more power. There is no downside to increased VP, except the initial cost of pumping up the pressure.
One more thing; with a manual trans, it becomes increasingly difficult to keep the engine running, as you come to a stop. Trying to drive 4 mph with street gears without riding the clutch is nearly impossible.But if your combo has lots of VP, then it is a lil easier, cuz the engine , if you can idle it down to 500/550 in gear, it will have enough power to do that. In fact it will have more than enough. It will have so much, that with a 223 FTH cam, it will start to buck and kick like a mule and try to twist off the driveshaft. The cure for that is to take out timing, to reduce the power, to stop the bucking.
If you have an automatic; all these points are still true, but now you don't have the clutch, so the stall has to be carefully matched to the VP, or else, with small VP, the bottom end gets real soft in a real big hurry. And you won't have the bucking issue at 4 mph.
For me,( 360 4-speed/3.55s) the switch begins right around 140. VPs in the 130s are not the end of the world, but you won't be bragging on that engine. 140 to 145 is a sweetspot, with enough low-rpm torque to have a lotta fun with. By 150, you are spinning tires right outta the gate, and in second gear @30 mph, it will light them up too.
I'm at 154VP/178psi roughly, and yes that 367 has more VP than it needs....... but it is so much fun, even with 3.23s. I could easily run 2.76s, and I have;just for kicks.
154VP is BB teritory
